1. Field of the Invention
The present invention relates generally to a current range control circuit, data driver, and organic light emitting display. More particularly, the invention relates to a current range control circuit configured to adjust a range of an input current, and a data driver and organic light emitting display employing the control circuit.
2. Discussion of Related Technology
Various panel display devices with reduced weight and volume as compared to cathode ray tube (CRT) display devices have recently been developed. Such panel display devices include Liquid Crystal Displays (LCDs), Field Emission Displays (FEDs), Plasma Display Panels (PDPs), and organic light emitting displays.
Among panel displays, organic light emitting displays are spontaneous emission devices that emit light by recombination of electrons and holes. Organic light emitting displays may also be referred to as organic electroluminescent displays. Like CRT display devices, organic light emitting displays have a high response speed compared with passive electroluminescent devices that require an additional light source, such as an LCD.
An organic light emitting display is driven by either a passive matrix method or an active matrix method. According to the active matrix driving method, the amount of current that flows through an electroluminescent device is controlled by an active device. Typically, a thin film transistor (TFT) is employed as the active device. The active matrix method is complicated, however it is advantageous in that the power consumption is small and emission time is long.
An organic light emitting display may employ a voltage programming method or a current programming method. According to the voltage programming method, a data driver outputs a voltage corresponding to a data signal, a capacitor of a pixel circuit stores the voltage corresponding to the output voltage, and an electroluminescent device emits light in response to the stored voltage. According to the voltage programming method, an LCD data driver may be used. However, it is difficult to obtain a uniform display using the LCD data driver due to deviations between the threshold voltage and mobility of the TFT used as the active device.
Using the current programming method, the deviation of the threshold voltage and mobility of the TFT are easily compensated for and thus a uniform display is obtained. Therefore, development of a data driver for outputting data current would be advantageous.
However, in the data driver of the current programming method, the range of the data currents may vary for different pixel circuits. For a pixel circuit that transmits current whose magnitude is equal to the magnitude of the data currents, the required range of the data currents is not large. However, when the data currents are multiples M of the current that flows through the electroluminescent device by using an M:1 mirror, the range of the data currents is large. Furthermore, since luminous efficiency varies with the type of electroluminescent device, the range of data currents required by the device may vary. Thus, because the required ranges of data current varies with the type of pixel circuit or the type of electroluminescent device, a particular data driver must be designed for each pixel circuit or each electroluminescent device.